During the Three Weeks, from 17th of Tamuz to the 9th of Av, we commemorate the conquest of Jerusalem, the destruction of the Holy Temple and the dispersion of the Jewish people.
Weddings and other joyful events are not held during this period; like mourners, we do not cut our hair, and various pleasurable activities are limited or proscribed. (The particular mourning customs vary from community to community, so consult a competent halachic authority for details.)
Citing the verse (Isaiah 1:27) "Zion shall be redeemed with mishpat [Torah] and its returnees with tzedakah," the Rebbe urged that we increase in Torah study (particularly the study of the laws of the Holy Temple) and charity during this period.
Links:
The Three Weeks
Some people think that if they were truly spiritual, they would never eat.
In truth, few acts are as divine as eating food.
Eating is similar to sifting gold. You grasp the divine spark within a food and reject the dross. And then, in the mitzvahs energized by that food, you carry that divine spark back to its origin within the oneness of its Creator.
That is why there are foods that are forbidden and foods that are permissible. The Hebrew word for “forbidden” is assur—meaning tied down. “Permissible” is mutar—untied.
Kosher means “fit.” Foods that are assur are not fit for the divine act of eating because the divine spark within them is tied down and cannot be released. If we would eat them, rather than carrying that spark upward, we would be pulled down with it.
But foods that are mutar are fit and ready to release powerful divine energy into all the mitzvahs we do.